Re: Question about satellite orbit classification

Gilberto,
At 01:47 PM 01/13/2000 -0500, Gilberto_Campos@email.whirlpool.com wrote:
>Someone asked me this question I could not answer, nor had I ever thought
>of that:
> -when is a sat called a Low Earth Orbit sat?
>
>More generally: what are the orbit classifications in function of
>perigee/apogee (apart from the obvious geostationary)?
According to algorithms used in SGP4/SDP4 propagation calculations, low
earth orbits have a period of less than 225 minutes. This calculates to a
little less than 6000 km for a circular orbit.
Personally, I think the definition is subjective, and could vary depending
on state of the art at the present.
We can't forget the Russian Comsat birds, which wing around at 1600
km. Are they LEO birds? I think so.
Typically, an amateur LEO satellite of the phase 2 variety will "see" less
than 10% of the earth at any given moment. A phase 3 bird will "see" more
than 25% of the earth, except at perigee, if the orbit is eccentric.
Would you like to know how the Federal Communications Commission defines LEO?
FEDERAL COMMUNICATIONS COMMISSION
47 CFR Part 1
[MD Docket No. 98-36; FCC 98-40]
Assessment and Collection of Regulatory Fees For Fiscal Year 1998
...
33. "Non-Geostationary" satellite orbits were first introduced in the early
90's with the filing of applications for non-voice, non-geostationary
satellite service operating below 1 GHz. These satellites proposed to
operate satellites in a "low earth" orbit, or a non-geostationary orbit The
term, "low earth orbit" was then synonomous with "non-geostationary". As
new technologies have evolved, we have received applications proposing to
operate in "medium" and "high" earth orbit technologies, also
non-geostationary orbits[, have been filed with the FCC]. Thus, we propose
to change the name of the "Low Earth Orbit Satellite Systems" fee category
to the "Non-Geostationary Satellite Systems" fee category in order to
clarify that non-geostationary satellites, whether operating in low, medium
or high orbits, are covered under this regulatory fee. This is consistent
with current industry use, as well as with Commission rules, which refer to
non-geostationary, not low earth, orbits and satellites. This name change
will have no adverse impact on any entity covered by regulatory fees in FY
1998.
...
So in essence, the FCC terms anything non-geostationary to be LEO.
Check
out: http://www.geocities.com/~saltillocib/sizepgs/geodef.html#anchor121819
This web site, maintained by Ricardo? has a good primer on sat orbits, the
distinction between LEO, MEO, and geostationary satellites. They claim:
"LEOs are either elliptical or (more usual) circular orbits at a height of
less than 2,000 km above the surface of the earth."
They define a MEO thusly: "Intermediate Circular Orbits (ICO), or Medium
Earth Orbits (MEO): ICOs are circular orbits at an altitude of around
10,000 km."
And a HEO as: "HEOs typically have a perigee at about 500 km above the
surface of the earth and an apogee as high as 50,000 km."
I don't really think this helps clarify much, but perhaps will allow you to
tender a better response!
73, Mike
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